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Are you searching for DCOM job? DCOM is Distributed Component Object Model is group of concepts by Microsoft and interfaces where client object program can request services from other server program and vice versa. DCOM is the technology for communicating between different software components which are on a network say Internet. Job opportunities are present everywhere for this position. DCOM job description might include having knowledge on concepts of various object models and network concepts. Wisdomjobs created interview questions exclusively for the candidates who are in search of job. If you are looking for job then go check out our DCOM interview questions and answers page to get more information on the kind and level of questions you will come across the interview.
In-proc server is a COM component, when instance is the server is loaded into the caller process space. In-Proc server can be easily identified by .dll extension.
Out-of-Proc server is a COM component that run in its own process space and for any instances created by the users, a proxy is created within the users process space. Proxy is responsible for interacting with the server to carry out operation on behalf of the client. (.exe extension).
For the first question, Yes, we can since the QueryInterface () rules of thumb suggest that if we can query an interface of C from B, we should be able to query the viceversa.The IUnknown implementation of both the objects has to do the 'magic'.
For the second question, Aggregation bounds outer and inner objects together and gives the user the interface pointers of either objects to access it directly so that the user never knows the objects are aggregated.
But when containment is used, the interface of inner object never exposed to the client directly rather the outer object receives the calls and forwards internally. Here also, the user doesn't know the objects are contained.
An object that implements the IMoniker interface. A moniker acts as a name that uniquely identifies a COM object. In the same way that a path identifies a file in the file system, a moniker identifies a COM object in the directory namespace.
OLE is a set of technologies to support linking and embedding. COM lies in OLE as one of the technologies. COM defines a binary standard / set of rules for developing reusable components.
To create the instance of COM componet use the following
To access the component that was there in local system use following API
To access the COM componet remotely use the following API
Returns a pointer to the current interface if successful or
IUnknown is a type of COM Interface.
Every COM class implements an interface named IUnKnown.
IUnKnown contains three methods:
Query Interface method is used to get the pointer to the interface specified in one of the parameters of this method. Client then uses this pointer to call the method of the component.
AddRef and Release are used to increase and decrease the count of the instance of component loaded in memory respectively. when the count reaches zero the component is unloaded.
Open the dll in dependency walker application(depends.exe).
If the dll is having following functions:
It is a COM DLL otherwise it is not.
CoInitialize will initialize the COM library and will move the executing thread to a STA or Single Threaded Apartment Apartment is the logical entity where threads live.
COM Dll exposes Interface on the contrary to normal DLL that exports functions. Clients create the pointer to COMDLL's interface to call the methods defined by the component that implements the interface.
That results in isolation of implementation and definition of method in the interface. Client doesnt need to relink or recompile the code if method in the com dll changes as far as the definition of the interface remains same.
COM (Component Object Model) technology in the Microsoft Windows-family of Operating Systems enables software components to communicate. COM is used by developers to create re-usable software components, link components together to build applications, and take advantage of Windows services.
In order to call your DLL as COM dll, you have to follow some rules to develop the dll. If those rules are there then only your DLL will be called as COM dll.
COM is a specification set of rules to develop binaries, COM is not a language.
Object references in COM is accounted using two methods of IUnknown Interface (AddRef and Release).
AddRef: Increments a reference count whereas "Release" decrements the count. When the count of the reference is zero the DLL is unloaded from memory.
There are two kind components:
We can use both as DCOM servers, its upto our design.
While accessing the DCOM component you have to provide COSERVERINFO structure. This structure is having the information about where the component is.
QueryInterface to A will delegate request to B which, in turn, will delegate request for the interface to C. This pointer will be returned to the client.
Queued Components, a key feature of COM+ and based on Microsoft Message Queuing Services (MSMQ), provides an easy way to invoke and execute components asynchronous. Processing can occur without regard to the availability or accessibility of either the sender or receiver. A home shopping network is an example of the type of application that might benefit from asynchronous processing. In this asynchronous, disconnected scenario where viewers phone in to several operators, orders are taken en masse and are then queued for later retrieval and processing by the server.
RCW is used for making a NET compnent talk to a com component. CCW is used for Com to .NET communication.
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